1. Field of the Invention
The present invention relates to reduced power consumption in home appliances and information devices having communication functions, and more particularly, to a peripheral device consuming less power with a part of its functions being operated intermittently, and a control method thereof.
2. Description of the Background Art
Infrared communication is often used as means of connecting control devices such as remote controllers and keyboards with controlled devices, in order to remotely control the home appliances and information devices, as well as to alleviate inconvenience of a wired connection.
Normally, the remote control devices such as remote controllers not only control the functions being provided while the controlled devices are in operation, including channel change, volume control, and command input, but also control switching on/off of the controlled devices.
If the controlled device is a home appliance, an infrared receive unit is normally incorporated therein in advance. However, information devices are often designed for general purposes.
IrDA Control is a system standardized by the Infrared Data Association (IrDA), a U.S.-based infrared communication standardizing organization, for remote control of home appliances and information devices, or for two way information exchanges. The IrDA Control system is controlled by the Universal Serial Bus (USB) system for versatility and ease of design when connected to or incorporated in an information device.
FIG. 1 illustrates connection between a PC incorporating a USB host controller and an external IrDA Control peripheral device (hereinafter, referred to as an "IrDA Control Dangle").
The USB host controller-contained PC 300 and the IrDA Control Dangle 302 are connected by a USB cable 301. The user can control PC 300 by an IrDA Control keyboard 303 or an IrDA Control mouse 304 which is connected to IrDA Control Dangle 302 by infrared rays.
Recently, a controlled information device, such as a personal computer, is designed to enter a sleep mode or a power OFF mode automatically or by the order of a user if it is not used for a long time period, to save power consumption.
However, even when the personal computer is in the sleep mode, the IrDA Control Dangle incorporated in, or connected via a USB cable to, the information device is designed to constantly function. Thus it is possible to recover the PC from its sleep mode by manipulating the IrDA Control keyboard, mouse or the like.
There are two possible ways to supply power to the IrDA Control Dangle. One is to directly supply power from the outside via an AC adapter or the like. The other is to supply power via the USB cable.
According to the USB Physical Layer Specification (Revision 1.1), a current up to 500 mA is supplied to a peripheral device through the USB cable when the USB host controller is in operation. Supplying the power through the USB is preferable because it is more convenient as the user does not need to ensure external power supply every time.
When the USB is in a sleep mode, however, the supply current of the USB is reduced to an average of 2.5 mA per second to save power consumption (the maximum standby current is permitted up to 100 mA if within 1 .mu.s). Therefore, there arises a problem that an IrDA Control Dangle consuming the current of greater than 2.5 mA cannot be made to function when the PC is in the sleep mode.